Conventionally, as a headup display device of this type, for example, there is known the one described in Patent Literature 1 listed below. The headup display device described in Patent Literature 1 is mainly composed of: a display for emitting display light; a reflection member for reflecting the display light emitted from this display; and a housing for housing the display and the reflection member, and is capable of projecting the display light reflected by the reflection member, to the projection member that is a front glass of a vehicle, through a light transmission part which is formed in the housing, and then, displaying a virtual image for an observer.
In this case, the reflection member is provided with: a concave mirror for reflecting the display light from the display; a mirror holder made of a synthetic resin, the mirror holder being formed in a shape of a substantially flat plate to hold this concave mirror; and position adjustment means for transmitting a motive power to a protrusion piece which is a motive power transmitted part partially protruded and formed toward the outside, and then, turning the mirror holder about a predetermined turning axle to thereby make it possible to adjust an angular position of the mirror holder.
This position adjustment means is mainly composed of driving means which is provided with a stepping motor for generating a rotation driving force by way of energization and a rotary shaft extending to this stepping motor, and in which a lead screw part which is a screw groove is formed on a peripheral face of the rotary shaft; a metallic supporting body made of a sectional substantial U-shape to fix and support the stepping motor in an immobilized state, and at the same time, to pivot a tip end of the lead screw part; a nut having a screw engagement part threadly engaging with a predetermined part of the lead screw part on an annular inner peripheral face, the nut reciprocally moving along an axial direction of the lead screw part by thrust imparted by rotation of the lead screw part; a guide shaft which is engaged with the supporting body so as to form a parallel state to the lead screw part; and a motive power transmission member in which a pair of abutment faces respectively abutting against both side faces of the nut is formed at a proximal part which is a base part, and a pair of protrusion parts made of a hemispheric shape so as to sandwich the protrusion piece of the mirror holder therebetween are formed on a pair of opposite walls protruding forward of the proximal part.
In so far as such structured position adjustment means is concerned, if the lead screw part is driven to be rotated concurrently with driving of the stepping motor, the nut that is threadly engaged with the lead screw part due to the rotation of this lead screw part reciprocally moves along an axial direction, and in synchronism with the reciprocal movement of this nut, for example, in one side face of the both side faces in the nut, in the pair of abutment faces, the thrust acts on one abutment face part on the side abutting against the abovementioned one side face.
Due to the action of the thrust as mentioned above, the motive power transmission member moves (reciprocally moves) along the axial direction in synchronism with reciprocal movement of the nut while the transmission member is guided by a guide shaft. Then, concurrently with the movement of the motive power transmission member, such a motive power as to turn the mirror holder about the turning axle is transmitted to the protrusion piece (motive power transmitted part) that is sandwiched between the pair of protrusion parts included in the motive power transmission member.
This fact means that the mirror holder and the concave mirror held on the mirror holder are turned by a predetermined angle about the turning axle due to the transmission of the motive power to the protrusion piece. In addition, the concave mirror is thus angularly moved, whereby the projection direction of the display light with respect to the front glass is adjusted, and concurrently with this, it is possible to move a position of a virtual image which can be visually recognized by an observer, in a vertical direction of the front glass.